Brain disease is becoming more prevalent in the aging population because of increased life span and Alzheimer's, Parkinson's, other dementias, and brain cancer will increase as US and European populations continue to age. Approximately 4,000,000 people in the U.S. have Alzheimer's disease. The US alone is expected to have 15 million Alzheimer's cases by 2050. Also an estimated 1.5 million people in the US have Parkinson's. Neurological brain disease affects 1% of Americans over 60 and each year there are 100,000 new cases. Diagnostic analysis of brain function represents an area of unmet need in the current imaging technology. Physicians require more specific and accurate information about brain function in addition to anatomy in order to diagnose a condition, prescribe treatment, and monitor results of intervention and treatment. Promising new drug therapies for Alzheimer's disease have been developed that can slow the progression of the disease. Nuclear medicine currently provides several molecular imaging modalities to assist with the assessment of brain function: Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT), and planar limited-angle tomography or simple planar single gamma imaging.
From the point of view of brain biology and imaging performance, including the physics of the process and imaging technique, PET is the first choice for the molecular brain imaging tasks for several reasons, including: 1) 18F-FDG brain imaging already serves as a sensitive method for diagnosis of Alzheimer's, 2) Pittsburgh Compound B (PIB) biomarker is expected to further improve early diagnosis of Alzheimer's, 3) many new PET radiopharmaceuticals for brain function imaging are presently under development to diagnose conditions before symptoms appear, 4) 4-5 mm resolution provided by current clinical PET scanners is less than half of that provided by clinical SPECT systems, and 5) the physical limit of the PET technique is around 1-2 mm while the typical spatial resolution obtained in SPECT imaging is about 10 mm due to the physical limits of mechanical collimators. However, at the current time PET's availability and cost are obstacles to fast widespread introduction while single photon labeled biomarkers can be made available in most practical situations due to their longer half-lives, no need for nearby production centers, and lower cost.
Tc-99m is the most popular label used in nuclear medicine with photon (gamma) emissions at ˜140 keV and with a convenient half-life of about 6 hours. The major problem associated with the single photon imaging procedure is that the characteristic gamma radiation from Tc-99m undergoes substantial absorption when traversing tissues such as brain. As a result for Tc-99m, the gamma ray flux, and the associated imaging signal in the gamma camera, coming from the sector of the head/neck away from the detector is much more attenuated than the gamma rays originating in the front part of the head.
With proper collimators and shielding, distribution of other single photon labels can be imaged such as I123, In111, Lu177, or I131. Except I123 (159 keV gamma emission), the three listed beta emitters are used in radiation treatment of cancer, also known as brachytherapy. In principle, therefore, the proposed method can also improve imaging of cancerous tissue in the brain/neck during treatment.
Neurological disorders that can be diagnosed by SPECT include traumatic brain injury, Alzheimer's, Attention Deficit Hyperactivity Disorder (ADHD), anxiety disorders, autism, bipolar disorder, depression, and obsessive-compulsive disorder.
What is needed therefore, is a mobile dedicated SPECT brain imager capable of producing high resolution images of the entirety of the patient's head, brain, and neck area. The dedicated imager geometry will include a reduced loss of imaging signals, which is commonly associated with conventional SPECT imagers, coming from the sector away from the detector as a result of attenuation of the gamma rays. By using SPECT imaging, the brain imager will take advantage of the longer half-lives of SPECT biomarkers which are more easily available at a lower cost than comparable PET biomarkers.